Photoelectric apparatus



Sept. 15, 1959 W. C. WHITE PHOTOELECTRIC APPARATUS Filed Dec. 11, 1952 Inventor: William C. White,

His Atoor ney.

United States, Patent PHOTOELECTRIC APPARATUS William C. White, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Application December 11, 1952, Serial No. 325,278

2 Claims. (Cl. 250-206).

This invention relates in general to photoelectric apparatus, and more particularly to combinations of photoconductive elements with electric lamps to constitute photoelectric control or translation devices.

Photoelectric cells can generally be classified, according to type, as photo-voltaic, wherein a voltage is actually generated upon exposure to light, as photo-emissive, wherein electron emission varies in accordance with the incident light, and as photo-conductive, wherein the conductance of the cell varies in accordance with the incident light. The invention is more particularly concerned with the photo-conductive type of cell generally comprising photo-sensitive semi-conductors which, in the absence of light, may be virtual insulators but which become electrically conductive in the presence of light rays such as rays in the visible light spectrum and adjacent infra-red and ultra-violet regions. An excellent photo-conductive element of this type is acadmium sulfide crystal substantially free from lattice distortion, as described in the copending application Ser. No. 190,801, filed October 16, 1950, of John Edward Jacobs, now Patent No. 2,706,790, entitled X-Ray Detection and assigned to the same assignee as the present invention.

An object of the present invention is to provide novel photoelectric translation and control apparatus.

Another object is to provide photoelectric control and translation apparatus of marked simplicity and comprising as principal elements a photo-conductive element and an electric lamp.

Yet another object of the invention is to provide photoelectric control and translation devices enclosed within sealed vitreous envelopes in unit constructions.

In accordance with the invention, a photo-conductive element such as a cadmium sulfide crystal and an electric lamp such as a neon glow lamp, are paired and arranged for mutual control. This is effected by physically arranging the photo-conductive element so as to be irradiated by the lamp, and by connecting both the element and the lamp in a common electrical circuit so as to achieve electrical reaction of the one upon the other. For instance, when a photo-conductive cell and a neon glow lamp having comparable voltage and current characteristics are so arranged and connected in a parallel circuit, a low frequency flashing of the lamp may be achieved, thus providing in effect an extremely simple form of flasher. If the cell and the lamp are connected in series, a photoelectric relay of a lock-in type results and which is extremely simple of construction. 'In accordance with other features of the invention, a combination of a photo-conductive element and a lamp may be sealed into a vitreous envelope, forming a unit structure having the advantages of simplicity, ruggedness and low cost.

The foregoing objects and other advantages and feaice tures of the invention will become apparent from th following description and accompanying drawings. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawing:

Fig. 1' shows a photo-conductive cell and a discharge lamp physically arranged for interaction and electrically connected in the basic parallel combination of the invention. I

Fig. 2 illustrates diagrammaticallythecorresponding series combination. I

Fig. 3 is a cross-sectional View of a sealed photoelectric unit connected in an arrangement corresponding to'that of Fig. l, the circuit connections being diagrammatically illustrated.

Fig. 4 shows a modification of the unit of Fig. 3 and connected in a modified series combination.

Referring to Fig. 1, a photo-conductive cell 1 and an electric discharge lamp 2 are physically disposed to achieve irradiation of the photo-cell by the lamp. The photo-cell, as illustrated, is similar to one described in copending application Ser. No. 312,761 of George E. Inman, filed October 2, 1952, entitled Photoelectric Device, now Patent No. 2,740,875, and assigned to the same assignee as the present invention. It comprises a cadmium sulfide crystal 3 which is supported-on lead wires 4 at the focal point of a silvered reflector type bulb 5 having a clear end face 6. As described in the lnman application, the crystal may be supported by pointing its ends and enclosing them in loops formed on-the ends of the lead wires, the junctures being coated with a suitable binder such as formed by the application of a colloidal suspension of carbon in alcohol. If desired the current rating of the. photo cell may be increased by filling the envelope 5 with a gas of high thermal conductivity such as helium to augmentthe heat dissipating capacity of the crystal. The photo-cell may conduct a current of the order of a few milliamperes with the application of 100 volts across it when irradiated, the current being substantially nil under dark conditions. I

The electric lamp 2 is preferably a discharge lamp having a striking voltage higher than itsoperating voltage. Asuitable lamp is a standard neon glow lamp of watt rating comprising a pair of electrodes 8 sealed within a glass bulb 9 containing neon gas at a pressure of a few millimeters. The spectral distribution of a neon discharge does not correspond with the peak spectral sensitivity of the cadmium sulfide crystal 3. In order to improve the efliciency of the system, the inside of the bulb 9 of lamp 2 may be coated with a phosphor providing a greenish light, for. instance a zinc sulfide phosphor having aspectral emission close to the optimum response wave-length of the cadmium sulfide crystal. The discharge lamp 2 may have a starting or breakdown voltage in the range from to volts (DC. or peak AC.) and an operating voltage drop of 50 to 60 volts with a current of a few milliamperes.

The photo-cell 1 and the lamp 2 are connected in parallel across a pair of conductors 11, 12 which lead to a pair of input terminals 13, one of the conductors, 12 in the drawing, being inseries with a resistor 14. The voltage applied across terminals 13 must be higher than the striking or breakdown potential of lamp" 2, and resistance 14 must have a value at least highenough to regulate the current through the lamp. For instance, the voltage at terminals 13 may be the usual to volts A.,C. commercial supply providing a peak voltage o pp ximate y 1 o ts. and sistan v 4 may h v a value of the order of megohm. Under these conditions, if the crystal is sufliciently illuminated from some outside source, for instance by daylight illumination, it by-passes such a large proportion of current that the voltage remaining after the voltage drop across resistance I4 is insuflicientto strike glow l'amp- If, however, the crystal is in darkness, then lamp 2 immediately' lights up but the radiation therefrom at once actuates the cadmium sulfide crystal of photocell '1 which in turn short-circuits lamp 2. Thus a relaxation circuit type of oscillation is set up. This oscillation will cease, of course, enough additional steady light reaches the photo-cell. The repetition or flashing frequency is quite low, generally a few cycles per second and is due in general to the inherent sluggish recovery of the cad mium sulfide crystal after its exposure to light. The frequency can be varied by changing the magnitude of the voltage applied at terminals 13 and the size of resistor 14. The range of repetition of frequency may also be extended in the usual fashion by connecting additional impedances in the circuit such as a resistor in parallel with discharge lampZ.

Referring to Fig. 2", the same photo-conductive device 1 and electric discharge lamp 2 are connected in a series circuit across input terminals 21 by means of conductors 22, 23 and 24. A resistor 25, which may have a value of approximately megohm, is connected into' condoctor 22 so as to be in series with the photo-cell and the lamp across terminals 21, and another resistor 26 which mayhave a value of a few megohrns is shunted across lamp 2. This combination may be termeda lock-in circuit; the circuit is static in the dark because insuflficient current is passed by the photo-cell to operate the lamp. If, however, the photo-cell is illuminated, eventor an instant, its conductivity increases and it passes enough current to strike-lamp 2 which thereafter illuminates the photo-cell whose conductivity is thereby maintained at a high level. The purpose of the resistor 26 shunting the lamp is to prevent the leakage current through the photo-cell under dark conditions, from strik ingthelamp and causing a weak glow.

Referring to Fig. 3 there is shown a sealed structure 31 including mounted therein a cadmiumsulfide'photoconductive crystal -3 and an electric discharge lamp such as adoubl'e-ended neon glow tube 32. As illustrated, the sealed unit is formed of a vitreous envelope of a typesimilar to the sealed beam reflector lamps in use for automobile headlights, and consisting of a rear paraboloidal internally silvered reflector 33 and a front lens 34. The cadmium sulfide crystal 3 is preferably mountedsubstantially at the'focal point'of the reflector, being supported on lead wires 35 welded intothe usual thimble' type seals 36. Three seals are used, one being common toone side of the crystal and to one side of the lamp: this arrangement makes it possible to connect the crystal and thelamp in parallel or in series as desired. In order toprovide for eflicient cooling of the crystal, a gas of high thermalconductivity such as helium may hesealed within the envelope formed by reflector 33 and lens 34.

InFig. IL-the unit 31 is shown with the elements corinected in a parallel combination, which combinationis connected in series with a resistor 37 across terminals 38. This arrangement corresponds to that illustrated in Fig.- 1 and will flash in a similar fashion. Theneon lamp 32 mm", if desired, also be mounted reasonably close to the focus of the reflector whereby the device 31,1nay serve as adirectional flasher. It. will also be appreciated, of course that device 31 may be connected in a series combination corresponding, to that of Fig. 2.

In Fig. .4, the unit 41 comprisesa vitreous envelope imilar to that of Fig- 3 and incl ding silvsIfidRfimmr 33 and front lens 34. However inorder to achieve a more economical construction, instead of including a sealed neon lamp within the unit, a pair of longer lead wires 42 are provided having bent inner end portions which support electrodes 43 in close proximity to each other. The vitreous envelope 41 is then filled with a suitable ionizable medium such as neon or a mixture of neon and argon at a low pressure. The cadmium sulfide crystal 3 is connected across one of the leads 42 and an intermediate lead 44. In order to prevent a glow discharge from occurring directly from one of the lead wires or electrodes to the crystal, a protective insulating sheath may be provided such as an insulating dielectric coating 45, shown as a fine speckling the drawing, covering the crystal and the adjacent portions of the lead or support wires.

The unit 41 of Fig. 4 may be connected in a parallel combination corresponding to the-arrangement of Fig. 1, or in a series combination corresponding to the arrangement of Fig. 2. As illustrated, the unit is connected in a series circuit includinga resistor 46, across terminals 47. The resistor 48 connected infparallehwith the'electrodes 43 prevent any glow across the elleetrodes'under'dark con ditions due to leakage current through the crystal 3. It will be appreciated, that as'so far 'described 'a-nd' with switch 49,"whi c-h may be used to connect acapacitor 50in shunt with the series combination'of eleetrod'es '43 and crystal 3, left open, the arrangementof Fig. "4 corresponds in general" to that of Fig. 2 and will remain static under dark conditions untiPiHuniinated by light from some extraneous source. If, however, the photo'- ele'ctric crystal is illuminated even momentarily, it will pass current and a glow'di'scha'rg'e will occur across electrodes 43, in turn illuminating the crystal and so" maintaining its conductivity. 1

;If however switch 49 is closed so as to connect capacitor Silinto the circuit, and on the condition that "a'direct current source of voltage is connected across terminals 47, the operation is modified and the electrodes 43' provide one flash of light which discharges capacitor 50 and then eiitinguishes itself. Thereafter the capacitor recharges slowly-from the voltage source through resistance 46 and the unit maybe flashed again by temporarily illuminating it from some outside source. Thus, the unit of Fig. 4 as connected and with switch 49 closed, operates as'a slave flasher which will respond with a singleflash of light each time itis momentarily illuminated but which will otherwise remain extinguished. i It willbe appreciated that under these conditions,- if; the. flasher unit of Fig. 3 is arranged to illuminate the unit of Fig. 4 the latter will respond with 'a single flash of lightfor every flash of the former.

While certain specific embodiments of the invention havebeen shown: and described, it will, of course, be appreciated that variousm'odifications may. be made. without departing from the invention. ,The specific. form and configurationof the crystal and of the lamp which have been described, and offlthe bulb into. which they are sealed, are to. be considered as illustrative only, d no as limitativ'e examples. .Thelappend d ela nsareac r ingly intended to ,coverany such. m dificati u comin within the true spiritand scope of the in ention.

- What. I claim. s new nd desire, t secur by, Letters .Patento e United Sta es is:

1. A photoele t c evic rc mpr tinsa seal d. vitreous .containerhaving reflec in su ace; l a w r reflec n into sai cqn ains a a: nh -s mi tt v we ti meat-l nd e c r c d h e .mwr rurreded Wit n, s i o taine km. sa e W re s i r t r d s a e m in marr e s an ia at the Q aLRP PH- said reflecting surface, andbeing responsive to radiat on .ptQduc edb y said dischargemeans.

2. A photoelectric device comprising a sealed vlt fious container having a reflecting surface, lead wires proa t 929 sai conta n a Pair 9 a s-t e a a photo-conductive crystal element supportedon said lead wires near the focal point of said reflectingsurface, an ionizable gaseous filling within said container, a protective sheath around said photo-conductive element insulating it from said ionizable filling, said photoconductive element being responsive to radiation produced by a discharge between said electrodes.

1,871,626 Macneil Aug. 16, 1932 6 Hoare May 2, 1933 Kwartin Dec. 5, 1933 Culver May 15, 1934 Waldschmidt Apr. 28, 1936 Braselton Mar. 19, 1940 Blackburn Apr. 15, 1941 Kelsey Mar. 7, 1950 Rose Jan. 15, 1952 FOREIGN PATENTS Great Britain Nov. 20, 1930 

